This invention pertains to a process for the preparation of 2-aryl-2H-benzotriazoles and derivatives thereof. More particularly, the invention relates to a novel process for preparing 2-aryl-2H-benzotriazoles whereby high yields of the desired products are obtained and effluent pollution problems occurring with present processes for making such products are essentially eliminated.
Heretofore, the conversion of an ortho-nitroazobenzene to the corresponding 2-aryl-2H-benzotriazole has been accomplished by chemical and electrolytic reduction processes. For example, as seen in U.S. Pat. Nos. 3,072,585 and 3,230,194, o-nitroazobenzene derivatives have been chemically reduced utilizing zinc in alcoholic sodium hydroxide solutions to give good yields of the corresponding 2-aryl-2H-benzotriazoles. Ammonium sulfide, alkali sulfides, zinc with ammonia at 80.degree.-100.degree. C, sodium hydrosulfide and zinc with hydrochloric acid have also been used as the chemical reducing agents for this transformation as disclosed in U.S. Pat. No. 2,362,988. The use of ammonium sulfide was also reported by S. N. Chakrabarty et al, J. Indian Chem. Soc., 5, 55 (1928); Chem. Abst., 23, 836, (1929) with mixed results depending on the presence or absence of substituent groups on the 2-aryl group. In some cases the desired 2-aryl-2H-benzotriazoles were not formed at all with the products of reduction being only the corresponding o-aminoazobenzenes.
Electrolytic reduction of o-nitroazobenzenes was reported by H. Itomi, Mem. Coll. Sci. Kyoto Imp. Univ., 12A, No. 6, 343 (1929); Chem. Abst., 24, 2060 (1930) with the use of a copper cathode in dilute sodium hydroxide solution. Yields varied from 25 to 60% depending on specific embodiments and conditions with a major impurity being formed, namely the corresponding o-aminoazobenzene.
The widely used zinc dust and sodium hydroxide chemical reducing system for transforming o-nitroazobenzenes into the corresponding 2-aryl-2H-benzotriazoles was reported by K. Elbs, et al, J. Prakt. Chem., 108, 204 (1924); Chem. Abst., 19, 514 (1925). The yields of the desired 2-aryl-2H-benzotriazoles varied from 30 to 85% depending on the specific o-nitroazobenzene intermediate reduced.
The known chemical and electrolytic reduction processes for preparing 2-aryl-benzotriazoles are not practical or economically attractive in many cases. The widely used zinc dust and sodium hydroxide system produces effluent pollution problems in respect to waste disposal of zinc sludge which is of increasing environmental concern.
This increased environmental concern has led to development of several new processes for preparing the 2-aryl 2H-benzotriazoles where pollution problems are mitigated.
In U.S. Pat. No. 4,001,266 the use of hydrazine hydrate was disclosed as a method of preparing the 2-aryl-2H-benzotriazoles by reduction of the corresponding o-nitroazobenzene or N-oxide intermediates.
The preparation in good yield of the isomeric, but chemically distinct 1H-benzotriazoles by the catalytic reduction in alkaline medium of o-nitrophenylhydrazine and selected phenyl ring substituted alkyl and perfluoroalkyl derivatives thereof was reported in Japanese patent publication, Sho 48-26012, Aug. 3, 1973. The isomeric 2H-benzotriazoles of this invention cannot be prepared from phenylhydrazines.
However, the 2-aryl-2H-benzotriazoles were prepared by the catalytic hydrogenation of the o-nitroazobenzene intermediates with hydrogen and various hydrogenation catalysts such as the noble metals, nickel and the like as seen in U.S. Pat. No. 3,978,074.
While hydrogen has classically been used in organic syntheses as a reducing agent involving a minimum of product isolation, pollution and other practical problems, another gaseous reducing agent, namely carbon monoxide, has been largely neglected.
In U.S. Pat. No. 1,237,828 the reduction of nitrobenzene to aniline is reported using a mixture of carbon monoxide and steam at high temperature (200.degree.-220.degree. C) and a mixed catalyst. Hydrogen is generated under these conditions, however.
Aromatic nitro compounds such as nitrobenzene are converted into the corresponding isocyanates by reaction with carbon monoxide at high temperatures and pressures in the absence of hydrogen and water. Various catalysts are used to aid this reaction as seen in Netherlands Patent 64/10490 where noble metal catalyst and 280 atmospheres pressure is used; in U.S. Pat. No. 3,576,836 where palladious halide plus an organonitrile is used as catalyst at pressures of carbon monoxide of over 100 atmospheres (see also F. J. Weigert, J. Org. Chem., 38, 1316 (1973)); in U.S. Pat. No. 3,461,149 where a noble metal plus a Lewis acid such as ferric or aluminum chloride catalyst is used with pressures of carbon monoxide over 1000 psi (67 atmospheres) (see also W. B. Hardy, et al, Tetrahedron Letters, 11, 961 (1967)); in U.S. Pat. No. 3,523,962 where noble metals plus organophosphorus catalysts and pressures of carbon monoxide over 33 atmospheres are used.
When such reactions are carried out in the presence of an alcohol, the isocyanate formed is converted in situ to a urethane as seen in Netherlands Patent 65/02601 and U.S. Pat. No. 3,338,956.
When nitrobenzene is reacted with carbon monoxide over an alumina catalyst at normal pressure, nitrosobenzene and azobenzene are formed while at higher pressure azobenzene is the main product. F. Glaser, et al Chem. Ing. Tech. 29, 512 (1957); Chem. Abst. 51, 17023h (1957) reports that water should be excluded as it promotes side reactions.
The effect of high pressure reactions of carbon monoxide on various aryl nitrogen compounds in the absence of a catalyst or a source of hydrogen atoms is reported by G. D. Buckley, et al J. Chem. Soc., 1949, 1154. It was found that nitrobenzene, nitrosobenzene and azoxybenzene are each reduced to azobenzene by use of carbon monoxide alone at pressures over 2500 atmospheres at temperatures over 200.degree. C and in the absence of a catalyst.
J. E. Kmiecik, J. Org. Chem. 30, 2014 (1965) reported that various aryl nitro compounds are reduced to either azobenzenes or to the corresponding amine compounds in the presence of carbon monoxide at high pressures (over 70 atmospheres) and at high temperatures (over 200.degree. C) in the presence of iron pentacarbonyl.
The reduction of nitroalkanes to oximes is disclosed by J. F. Knifton, J. Org. Chem. 38, 3296 (1973), (German Offen. 2,019,261), using copper salts solubilized in alkylpolyamines in the presence of carbon monoxide. Highly basic amines are preferred such as 1,3-propanediamine and 1,6-hexanediamine.
The reduction of nitrobenzene to aniline is reported in U.S. Pat. No. 3,290,377 by use of carbon monoxide at pressures up to 100 atmospheres in the presence of copper salt-amine complex catalysts at moderate temperatures. The yield of aniline was very dependent on the nature and concentration of the copper salt-amine complex catalyst.
The prior art disclosure of reductions of aromatic nitro compounds using carbon monoxide is largely limited to the simple reduction of nitrobenzenes to the corresponding azobenzenes or anilines. There is no teaching that a simultaneous reduction and cyclization of o-nitroazobenzenes to 2-aryl-2H-benzobriazoles are possible or feasible using this special reducing agent. Indeed it is taught that olefinic double bonds are unaffected by the use of the copper salt-amine catalyst/carbon monoxide reduction system.
It is therefore an object of this invention to provide a novel process for the preparation of 2-aryl-2H-benzotriazoles avoiding severe pollution and environmental problems.
A further object of this invention is to prepare 2-aryl-2H-benzotriazoles by reducing and cyclizing the corresponding o-nitroazobenzene under certain conditions hereinafter set forth in greater detail whereby high yields of the products can be obtained in acceptable purity.